In a non-contact power supply system which contactlessly supplies power to a battery mounted in an electric vehicle or the like, a power transmission coil provided on the ground and a power reception coil mounted in the vehicle are arranged to face each other and the power transmission coil is excited to supply power to the power reception coil. In such a non-contact power supply system, the power reception coil needs to be aligned to face the power transmission coil; and a system disclosed in Patent Literature 1 has been conventionally known.
In Patent Literature 1, the power transmission coil is excited at lower voltage than normal power supply voltage and power received by the power reception coil is detected to determine whether the power reception coil is present at a desired position relative to the power transmission coil.